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Global-scale variations of the ratios of carbon to phosphorus in exported marine organic matter

Abstract

The ratio of carbon (C) to phosphorus (P) in marine phytoplankton is thought to be constant throughout the worlds’ oceans. Known as the Redfield ratio1, this relationship describes the links between carbon and phosphorus cycling and marine ecosystems2,3,4. However, variations in the stoichiometry of phytoplankton have recently been identified, in particular strong latitudinal variability5. Here we assess the impact of this variability in the C:P ratio of biomass on the C:P ratio of organic matter that is exported to the deep ocean using a biogeochemical inverse-model based on a data-constrained ocean circulation model6,7 and a global database8,9 of dissolved inorganic carbon and phosphate measurements. We identify global patterns of variability in the C:P ratios of exported organic matter, with higher values in the nutrient-depleted subtropical gyres, where organic matter export is relatively low, and lower ratios in nutrient-rich upwelling zones and high-latitude regions, where organic matter export is high. This suggests that total carbon export is relatively constant throughout the oceans, in agreement with recent estimates of carbon fluxes10. We conclude that the latitudinal patterns of C:P in exported organic matter are consistent with the large-scale stoichiometric variations in phytoplankton C:P. We suggest that a future expansion of nutrient-depleted waters could result in a shift to more efficient C export that compensates for the expected decline in productivity.

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Figure 1: Map of (C:P)exp values inferred from the inverse model.
Figure 2: Layer-averaged root mean squared (r.m.s.) DIC misfit (μmol C kg−1).
Figure 3: Comparison of the C:P ratio of suspended particulate organic matter (POM) to that of exported organic matter.
Figure 4: Experimentally determined export production at six sites from Table 2 of ref. 9.

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Acknowledgements

This work was supported by grant ER65358 from the US Department of Energy Office of Biological and Environmental Research to F.W.P. and J.K.M. A.C.M. and M.W.L. acknowledge support from NSF Dimensions of Biodiversity program and F.W.P. also acknowledges support from the National Science Foundation grant OCE-1131768.

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Y-C.T., F.W.P. and A.C.M. initiated this study. Y-C.T. and F.W.P. formulated the inverse problem and carried out the model inversions with advice from A.C.M. and J.K.M. M.W.L. provided the BATS sediment trap data. Y-C.T. and F.W.P. wrote the paper with input from A.C.M., J.K.M. and M.W.L.

Corresponding author

Correspondence to François W. Primeau.

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The authors declare no competing financial interests.

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Teng, YC., Primeau, F., Moore, J. et al. Global-scale variations of the ratios of carbon to phosphorus in exported marine organic matter. Nature Geosci 7, 895–898 (2014). https://doi.org/10.1038/ngeo2303

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